This invention relates to antenna systems having means for rejecting unwanted interference signals, and in particular to systems of that type that are suitable for monopulse radar applications and that utilize coaxial cable circuitry and orthogonal dipole radiating elements.
The capability for polarization control in antennas offers obvious advantages not only for such applications as optimizing signal strength over communication paths and reducing the scintillations of signals from radar targets, but also for receiving a desired signal while rejecting interfering ones of a differing polarization. In the past, however, the complications of achieving variable polarization have prohibited realization of its advantages in phased arrays. Recently an electronic method has been developed that is sufficiently simple for use in phased arrays. With this new method, the polarization of phased arrays can be rapidly varied through any linear, either circular, and even general elliptical forms.
Although such a method, in principle, expands the utility of interference rejection systems, to date, implementation of the method has been realized only with slot antennas and waveguide feed circuits. In order to effectively apply such techniques to monopulse radar systems considerable circuit simplification is required. Furthermore, means for effecting the results of this method with coaxial cable circuits and separately fed orthogonal dipole antenna elements are essential to such simplification. Such means are not now available. There currently exists, therefore, the need for apparatus and techniques effective to provide simplified interference rejection capabilities in phased array antenna systems and in monopulse radars. The present invention is directed toward satisfying this need.